1. Field of the Invention
The present invention relates to a method of fabricating a semiconductor device, and more particularly, to a method of forming a metal line in a semiconductor device.
2. Discussion of the Related Art
Generally, a process of forming a metal contact is essential to fabricating a multi-layer semiconductor device. The metal contact may form a base of a vertical line between upper and lower conductor layers. Meanwhile, as the space for the contact is reduced according to the high integration of semiconductor devices, an aspect ratio of a contact hole increases. Hence, the metal contact forming process becomes more difficult and important.
Despite its poor property of filing up a contact hole, aluminum, which has low specific resistance and can be easily provided, is one of the most popular contact materials. Yet, as the space for the contact is abruptly reduced, it is no longer feasible to fill the contact hole with only aluminum anymore.
Hence, a metal line forming process using a tungsten plug, which has a very good property with respect to filling gaps, despite its specific resistance relatively higher than that of Al, together with an Al line has become popular.
FIGS. 1A to 1F are cross-sectional diagrams of a process of forming a metal line according to a related art, in which a general tungsten plug forming process is applied to forming the metal line.
Referring to FIG. 1A, a metal line 102 is formed on a semiconductor substrate 100 provided with various devices therein. An insulating interlayer 104 is formed over the substrate including the metal line 102 and is then made smooth. A prescribed portion of the insulating interlayer 104 is selectively etched to form a contact or via hole 106 exposing part of the metal line 102.
Referring to FIG. 1B, a first metal layer 108 is formed on the insulating inter layer 104 including an inside of the contact or via hole 106. In this case, the first metal layer 108 is formed of a liner barrier metal such as Ti/TiN.
Referring to FIG. 1C, a tungsten layer 110 is deposited on the first metal layer 108 so that the contact or via hole 106 can be filled up with the tungsten layer 110.
Referring to FIG. 1D, the tungsten layer 110 is etched back to form a tungsten plug 110. After the contact or via hole 106 has been filled up with the tungsten layer 110, CMP (chemical mechanical polishing) is carried out on the tungsten layer 110 and the first metal layer 108. A touch-up process is then carried out on the substrate 100 to remove tungsten residue remaining on the insulating interlayer 104, whereby the tungsten plug 108 filing up the contact or via hole is completed.
Referring to FIG. 1E, a second metal layer 112, a metal layer 114, and a third metal layer 116 are sequentially deposited over the substrate 100 including the tungsten plug. Photoresist is coated on the third metal layer. Exposure and development is carried out on the photoresist to form a photoresist pattern 118 defining a metal line over the tungsten plug. Specifically, the second and third metal layers 112 and 116 are preferably formed of Ti/TiN. The metal layer 114 as a main line material may be formed of aluminum.
Referring to FIG. 1F, dry etch is carried out over the substrate including the third metal layer 116, the metal layer 114, and the second metal layer 112 using the photoresist pattern 118 in FIG. 1E as an etch mask. Hence, a metal line consisting of the second metal layer 112, the metal layer 114, and the third metal layer 116 is completed. Thereafter, the photoresist pattern is removed.
However, in the related art method of forming the metal line, the touch-up process for forming the tungsten plug after CMP for insulating layer smoothing scratches a surface of the insulating interlayer 104 or rips out the insulating interlayer 104 provided with the contact or via hole 106.